Evolution Of Coastal Geomorphology And Influence Mechanism Of Headland Bay Along Eastern Laizhou Bay

In view of the violent human activities and the significant changes of sediment transport,we studied the morphodynamic evolution and influence mechanism of erosional sandy coast along the eastern Laizhou bay which is regarded as a unitive coast system made up of four neighboring headland-bays with the comprehensive usage of several relevant methods,such as field investigation,3S(RS/GPS/GIS)technologies,sediment analysis,numerical coast morphological analysis,numerical hydrodynamic model and.it has been significantly changed from four headland harbors,using field survey,3S(RS / GPS / GIS)technologies,digital coast analysis,numerical simulation and equilibrium shoreline estimation.The main research contents included the coastal morphological evolution,coastal erosion-sedimentation changes,and coastal morphological response to human activities of the eastern Laizhou bay in recent sixty years.We have discovered the affecting mechanism of river sediment load decrease and land use/land cover change in the supratidal zone on coastal geomorphic evolution of the coast firstly,investigated the morphological erosion-sedimentation change background,evolution history and differences of spatiotemporal of coastal erosion secondly,and establishing a morphodynamic evolution model of the erosional sandy coast along the eastern Laizhou bay in recent sixty years thirdly.The main conclusions included:(1)The basic geomorphic features of the eastern coast of Laizhou Bay are both headland and straight coast.On the 60-years scale,the coastal morphological characteristics oscillated between headland bay and straight coast,leading to frequent changes in alongshore sediment transport rate.In the natural state,the instability value of Qimudao-Shihuzui(11.15%)is largest among each headland bays,and the instability values of the three downstream headland bays decrease in turn.In the case of sediment loss or disappearance,the coastal erosion of the Qimudao-Shihuzui bay is the most significant.Especially in the vicinity of the mouth of the Jihe River,erosion back to 2.31 km.The erosion of the cover segment of the four bays is more severe than the tangential section.It takes 30 years for the coastal system to adjust the sediment reduction of the river into the sea.The effect of reduced sedimentation on the time of shoreline adjustment to dynamic equilibrium is not significant.The effect of the change of sediment volume into the sea was significant difference among different segments.(2)The characteristics of the time course of shoreline migration were non–linearity,showed the alternately erosion and sedimentation.From 1959 to 2013,the proportion of erosion shoreline fluctuated,divided into two stages in 1985.The differences in the spatial distribution of shoreline migration were not consistent with the overall changes in the coastline of the headland Bays.In addition to the Sanshandao-Diaolongzui section,the other three headland bays in the ten-year scale shoreline evolution showed scouring and silting alternate distribution pattern.And Sanshandao-Diaolongzui section,although the rates of different periods were significant differences,the coastline has always been shown siltation or balance.The evolution of underwater slope and shoreline was in close contact.The shoreline of the coast is advancing to the sea as a whole during the period of 1959-1985.The water depth of the contours of 2m,5m and 10 m were also shallow.The area of siltation was 1.87 × 10~8 m~2.The volume of sediment was 1.15 × 108m3.The shoreline of the coast is erosion as a whole during the period of 1985-2006.The water depth of the contours of 2m was increase,5m was equilibrium and 10 m shallow.The area of siltation was 5.58 × 107m2.The volume of sediment was only 8% of the original period.The continuous erosional band of underwater was emergence in the majority of the shoreline outside the coastline.(3)The particle size analysis of the buried samples showed that the sedimentation types belonged to medium and coarse sand,and the degree of sorting was moderate – good.The skewness were positive and extreme positive.66.67% of the samples were shallow sea sediments.At present,the release of shallow sediments indicates that the shore is in an eroded state.The particle size analysis of the 148 surface sediments showed that the average particle size was mainly coarse sand,medium sand and very coarse sand,and the sorting degree was mainly good and medium.The average particle size of the profile located in the vicinity of the mouth of Jiehe River(medium sand,coarse sand and gravel)was the coarsest,and gradually reduced to the downstream.(4)Large-scale construction of reservoirs in the upper reaches of the river resulted in a decrease in the amount of sediment into the east coast of Laizhou Bay,which significantly changed the geomorphic evolution.The results of numerical simulation of hydrodynamics show that the erosion effect of the east coast of Laizhou Bay is increasing with the decrease of sediment concentration in the river,and the erosion extent is enlarge and the intensity of erosion is increasing.There have been different scouring and silting conditions in different sections.The erosion bands are mainly distributed between 2m and 5m isobaths,and the more serious the erosion where near the estuary.However,in addition to the strong erosion of the estuary of Jiehe River,Wanghe River,and southwestern of Diaolongzui,the entire east coast of Laizhou Bay shallower than 2m isobaths are in the state of equilibrium of scouring and silting or slightly siltation.(5)The main evolution trend of land use along the eastern coast of Laizhou bay is the transition from aeolian sandy land,woodland and farmland to aquaculture ponds and residential land.A belt zone of aquaculture facility parallel to the coastline has been formed and dykes are constructed along the outside of the coastal aquiculture zone.The significant land cover change in the supratidal zone has profoundly modified the boundary conditions of storm surges.The hydrodynamic modeling results show that the ocean dynamics near the coastline are enhanced and caused severe erosion of the coastline,beach and underwater coastal sea slope along the eastern coast of Laizhou Bay.(6)The upstream control point of headland bay was changed by the Longkou Artificial Island Phase I project,which resulted in the significant changes of the rate and direction of coastal sediment transport.According to the simulation results of the one-line model,the direction of the sediment transport in the east of the estuary of the Jiehe River estuary was reversed(from NE-SW to SW-NE).The cover area of the Artificial Island was in the state of siltation,and the downstream section was strong erosion(from the eastern of Jiehe estuary to the southwestern of Zhuliuhe estuary 1.5km).The simulation results of the static equilibrium shoreline from the parabolic model show that the shoreline near the Jiehe estuary and its southwest coastline will be eroded and retreated.The headland of Shihuzui will be deposition.The result of strong erosional section is consistent with the one-line model.(7)The evolution of siltation and sedimentation on the east coast of Laizhou Bay was significant instability.The distribution of erosion and silt section was spatiotemporal alternate during different times,in different sections.The coastal geomorphic erosion and sedimentation evolution is unstable at least on the 60-yeard scale,under the control of the coastal boundary conditions,and coupling with the high frequency of storm surge.In the last 60 years,there have been at least 5 times of coastline advancement and the rate of scouring and silting changing,and an average frequency of 10 years,and the different sections are not synchronized,under the joint action of the sediment exchange between beach-submarine bar,the conversion of headland bay and straight coast,the construction of reservoir,industrial aquaculture in supratidal zone and coastal engineering.The trend of scouring and silting in the future 50-year scale is the alternative of erosion and deposition on the background of the overall erosion.